1,721,068 research outputs found
The effective stiffness of a nanoporous rod
No full textA study was conducted to analyze the influence of surface effects on the elastic characteristics of nanoporous materials. Two models were considered, such as one based on taking into account the surface stresses and the other using the approach of the theory of composite materials. This approach involved taking into account the surface effects due to the surface layer of finite thickness with elastic moduli differing from those of the basic material. The increase or decrease in the rod stiffness depended the relation between the elastic moduli of the surface layer and the matrix. The effective stiffness decreased and increased with decreasing pore radius. A complex model combining both the presence of surface stresses and the surface layer with the properties that differ from those of the matrix was proposed on the basis of these two approaches
On equations of the linear theory of shells with surface stresses taken into account
No full textWe construct equations of equilibrium and constitutive relations of linear theory of plates and shells with transverse shear strain taken into account, which are based on reducing the spatial elasticity relations with surface stresses taken into account to two-dimensional equations given on the shell median surface. We analyze the influence of surface elasticity moduli on the effective stiffness of plates and shells
Surface viscoelasticity and effective properties of thin-walled structures at the nanoscale
No full textWe discuss the influence of surface viscoelasticity effects on the effective properties of materials such as effective bending stiffness of plates or shells. Viscoelastic properties in the vicinity of the surface can differ from the properties of the bulk material. This difference influences the behavior of nanostructural elements. In particular, the surface viscoelastic stresses are responsible for the size-depended dissipation of nanosized structures. Using the extension of the Gurtin-Murdoch model and the correspondence principle of linear viscoelasticity we derive the expressions of the stress and couple stress resultant tensors for shear deformable plates and shells
Linear theory of shells taking into account surface stresses
No full textA study was conducted to obtain the equations of equilibrium and constitutive equations for the stress resultants and couples tensors while taking into account the surface stresses acting on the shell surfaces. The equations were obtained generalizing the results to the case of the linear theory of elastic shells taking into account the transverse shear. The effective shell stiffness, specifically the bending stiffness Deff depended on the surface elastic moduli, which is substantial for nanodimensional thicknesses. The variational method was used for the formulation of boundary-value problems of the theory of elasticity with surface stresses. Constitutive equations also made it possible to write the equilibrium equations for the shell and plate with taking into account surface stresses in terms of displacements and rotations
On free oscillations of an elastic solids with ordered arrays of nano-sized objects
No full textWe discuss free oscillations of some elastic structures consisting of an elastic substrate and an ordered array of aligned nano-sized objects. Considering various shapes of nano-objects such as beams, tubes, and spheres, we investigate the spectrum of eigenfrequencies of these structures in comparison with the spectra of one nano-object and of the substrate. As a result, we find the correspondence between the spectrum of whole structure and the spectrum of one nano-object, which gives the possibility to determine few first eigenfrequencies of nano-sized objects
Modeling of spiral nanofilms with piezoelectric properties
No full textA modal analysis of a two-layer nanofilm with piezoelectric properties was performed. Eigenfrequencies were determined and eigenmodes corresponding to them were constructed. The effect of the surroundings on the eigenfrequencies was analyzed
Some problems of nanomechanics
No full textThe paper presents a selection of simulation results obtained for nanosized objects in continuum and structural mechanics. Eigenfrequency measurements as a tool to study nanostructures composed of a multitude of like nanoelements are discussed. The structures under consideration are ordered arrays of nanoobjects (nanocrystals, nanoshells) fixed on an elastic substrate. It is shown that from the eigenfrequency spectrum of this type of mechanical systems one can determine several eigenfrequencies of a single nanoobject. Also considered in the paper is accounting for surface stress and associated modification of effective properties of nanomaterials
The influence of surface tension on the effective stiffness of nanosize plates
No full textThe problem of bending of a nanosize plate, taking into account the action of the surface effects, is considered, and the influence of surface tension on the effective stiffness of nanosize plates is found. The deformation of a linearly elastic body is considered and the action of the surface effects on the upper and lower surfaces are taken into account. An approximation for the field of displacements that is linear in thickness is assumed to describe the deformations of the plates. The equations of state allows the determination of the equilibrium equations for the plate, with the surface tension being taken into account, in terms of the displacements and rotations. The dependence of the transverse shear forces and momentum tensors on deformations is defined by the four elastic constant
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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